To accurately reproduce a desired target color using a printing system, an operator must perform repeated color adjustments by trial and error. In particular, the operator might adjust the color of an image on a video display in an attempt to obtain the desired target color on a color printer. After printing that first image using the color printer, the operator must perform a second color adjustment on the video display, wherein the adjustments are based on observations of the first printed image. This process would be repeated until the desired color print is output.
Such trial and error generally involves the process of color separation. In the past, color separation has traditionally been a matter of deciding what quantities of each of several inks (or other colorants) to use to achieve a given color. While this functionality was originally a photochemical process involving colored filters, it has evolved to its current state, which utilizes look-up tables comprising colorimetric input values or input values in a device color space. The output values for the tables may be n-dimensional ink vectors, where n is the number of inks used by the printer and the vector components represent quantities of each ink available on the color printer. In practice, the current approach utilizes these tables to transform ink amounts for each color plane, thereby reproducing the desired target color.
However, controlling print color by variation of ink amounts is a highly non-linear process, deriving from a complex relationship between changes in the quantity of each ink color used and the color of the resulting printed ink combination. As a result of this non-linearity, the gamut (the set of all printable colors) of a printing device may also include concavities. These concavities in some cases result in only relatively dull dark colors being printable. In addition, small changes in a system comprising non-linear relationships may also result in unacceptably large changes in output color. Therefore, non-linear relationships in a printing system may make it very challenging to obtain printing properties such as smooth transitions between colors, low cost per copy, high color constancy, and low grain.
In current systems, options are available for printing using lower amounts of ink. Present methods of using lower amounts of ink include using relatively more available black and/or dark inks and relatively less of a system's light inks. In one method more black is applied at the ICC (International Color Consortium) profile generation stage. Another way is to use a given ICC profile wherein the generated standard CMYK (Cyan Magenta Yellow Black) output is analyzed and some of the CMYK vectors are substituted by other vectors that use more black (K) ink and less ink overall. These methods oftentimes lead to an increase of grain, and/or change the color gamut.
In another method the available color gamut is reduced so as to reduce ink usage. Because ink usage may be relatively high near the outer borders of a color gamut, reducing the color gamut facilitates reduced ink usage. However, this method also reduces the availability of the colors near the outside borders of the gamut.
One of the objects of this disclosure is to find and use a system's optimum performance for particular print attributes, for example any halftone property such as low ink usage.